Rheostat



Patented Mar. 8, 1927.

UNITED JOSEPH A. ROSTRON, OF CAMBRIDGE, MASSACHUSETTS.

RHEOSTAT.

Application filed March 7, 1922'.

This invention relates to improvements in rheostats. While the inventionmay be applied in various connections, the apparatus is illustrated moreparticularly as it may be applied for use with *acuum tube units insending and receiving wireless messages. In a so called wirelessinstallation it is necessary to be able to adjust the resistance withgreat delicacy. Although various devices have been proposed heretoforeto accomplish this purpose they have always, so far as I am aware,entailed the addition of elements and construction which introdu'cedmore complications and cost. It is a purpose of the present invention toprovide for such delicacy of adjustment while retain ing extremesimplicity of parts. And whereas it has been .attempted to attaindelicacy heretofore by providing a considerable number of convolutions,and making these convo'lutions small, so that the step from one toanother would be small, the present invention provides for making theresistance wire convo'lutions of any size, with a micrometer adjustmentinstantly available along any of them,

These objects are accomplished by providing a straight helix ofresistance wire in which the convolutions are separated from each othera small distance, as, for example about 1/64 or 1/32 of an inch, andproviding a rod which is mountedslidably and rotat ably .at its axiscarrying a brush or contact member which is capable both of sliding toand fro crosswise of the convolutions, moving in the direction of theaxis, and also is capable of moving around in the (llI'CtlOII of theconvolutions, circling around the axis following the thread of thehelix. The parts are so constructed that the brush is frictionally heldat any of its positions, preferably by friction of the brush on thecoil. Specifically, this is accomplished by making the brush of a flatspring metal strip, which strip is arranged outside of the coil,extending in a direction parallel to the axis and close over the threadsof the coil, with a shoe atits end which is convex toward the coil andrests in contact therewith, with the convexity of the shoe pressing intothe space between two adjacent convolutions of the coil and makingcontact with both of them. This brush is mounted on a rod which is setat the axis of the coil and is slidable to and fro in the direction ofthe axis, moving Serial No. 541,760.

the shoe with it from one convolution to another when the rod is so slidby the operator, on which occasion the convexity of the shoe allows iteasily to ride up over each successive convolution and spring into thevalley or depression beyond it. It is a feature of the invention thatthe shoe sinks deeply enough between the adjacent convolutions to tenddefinitely to remain between them, and consequently to remain betweenthem when the rod on which it is mounted 1S rotated without being pushedin the direction of the axis. A control button being provided for theoperator to grasp the rod, he can both push the rod so that any desirednumber of convolutions of the resistance wire are included in thecircuit, and can rotate the same control means to add thereto orsubtract therefrom any desired fraction of a convolution. The shoe maybe formed by the extremely simple device of making a bend in the thinsheet metal which constitutes the brush. Variations may however be madein this respect and in other respects without departing from the scopeof the invention. It is intended that the patent shall cover, bysuitable expression in the appended claims, whatever features ofpatentable novelty exist in the invention disclosed.

In the accompanying drawings,

Figure 1 is a rear view of a rheostat constructed in accordance with thepresent invention Figure 2 is a side view of the device as seen from theright in Figure 1;

Figure 3 is a section on line 33 of Figure 1;

Figure 4c is a section, somewhat enlarged, through a portion of the coilshowing the contact relation of the brush and the wires; and

Figure 5 is a section on line 55 of Figure t on the same scale as isused in that figure.

Referring to the drawings, the device is shown assembled on a base orpanel 10 which may be considered to be the equivalent of any portion ofa wireless apparatus adapted to support a rheostat. The circuit whoseresistance is to be controlled by the apparatus of the invention leadsthrough a terminal and contact plate 12 to which is attached, by a screw16, one end 18 of a coil 18 of resistance wire wound helically about aninsulating cylindrical surface 19,

preferably formed of heat resisting material. Each turn of wire of thishelix is a short distance away from the next, thereby forming betweeneach two adjacent convolutions a sort of helical groove around thecylindrical surface.

In the embodiment of the invention illustrated, this surface 19, uponwhich the coil is wound, is a sleeve 22 of non-conductive materialplaced around a barrel or drum 24 which may be of any size suitable tothe requirements of the apparatus being served, so that much or littleresistance wire may be wound about it as needed. Within the drum at eachend, and secured to it, is a diametrical cross bar. One of these, 26, inconjunction with the screws 30, serves to hold the drum firmly on thepanel 10, and the other, 28, serves several purposes, among which is thereinforcing of the drum and the providing of a convenient place forattachment of the other end 18 of the coil, there being a screw 82 onthe cross bar for this purpose. The drum may be made of any suitablematerial, but the cross arm 26 should be of conducting material and thecross arm 28 of insulating material, so that upon the attachment of theend 18 to the latter the path of current, thus far described isterminated. It is also desirable to stop the windings a short distancefrom the end of the cylindrical surface 19, as will more particularlyappear hereinafter and to this end a hole 33 through the drum isprovided for passage of the wire to the arm 28. If the drum is ofconductive material provision should be made for insulating the walls ofthis hole to prevent any contact with the wire. The cross bar 26, isconnected by a short conductor 34 to the other contact plate andterminal 20, and it only remains to describe the means by which thecurrent is conducted from the coil to the cross bar 26 and to show howthese means may be utilized to regulate the length of the current path;first by changing the number of complete convolutions of the coiltraversed by the current, and second by adding or subtracting a portionof a single convolution to or from the number of complete turns in thepath. This is accomplished by providing a brush or wiper member 36 whichcan be moved axially along the surface of the drum from one turn of thewire to the next and circumferentially around the helix along any oneconvolution. The brush is preferably made of flat spring metal with acurved foot or shoe 36 formed by bending the end of the brush to providea convex ridge on the side of the brush next to the wires. This shoedips into the space or groove between two successive turns of the wireand is held there by its own spring pressure or resiliency. Thecurvature of the surface of this foot is about an axissubstantially atright angles to the axis of the coil, and the radius of curvature issufficiently large to enable the shoe to be moved across the wires withlittle effort, yet is small enough for the shoe to drop into each grooveand thus prevent undue slippage. When thus resting in a groove the shoeis tangent to the surface of the wire, see Fig. 4L, which enables it tobe turned around the helix, in either direction with little friction.The arm of the contact brush rearward, extends approximately parallel tothe axis of the coil, a distance slightly greater than the length of thedrum, and then turns toward the axis where it is fastened to a rod 38which lies along the axis of the drum. This rod passes through a hole inthe rear cross bar 28, which helps support it, and thence through thedrum and the other cross bar 26, and the panel and is movable rotatablyand longitudinally. The end of the rod projecting on the front of thepanel is provided with a knob 40 by which the rod can be pulled out orpushed in or rotated in any of its axial positions. The axial rod ismade of conducting material and makes sliding fit with the cross bars sothat when the foot is in contact with the helix the rear part of thecoil is short circuite'd through the brush and its arm to the axial rod38 and thence through the arm 26 and conductor 3% to the terminal 20.The circuit will be broken at any time when the shoe of the brush restson the insulated surface 19 beyond the last convolution. This simpleprovision enables the rheostat to perform the function of a switch, andin this form it is especially adapted for certain uses such as dimminglights, the complete extinguishment being a natural step just beyond themaximum dimming.

It is obvious that any movement of the rod axially or in rotation mustmove the contact brush similarly. If toward or from the panel the lengthof resistance wire in circuit will be successively shortened orlengthened by units equalling the length of I a convolution. A fairlyclose adjustment of the rheostat can be made by simply mov ing the rodaxially. The exact resistance needed is then attained by turning theknob in either direction so as to wipe the foot of the contact brusharound the helix, thereby increasing or decreasing the path of thecurrent through the coil by whatever fractional part of a singleconvolution is thus added or subtracted. The dotted positions of thecontact arm shown in Figure 1 illustrate two of the various positions inwhich this arm may be rotated about the coil. drum surface may be madein any size practicable it follows that the greater the circumference,the finer will be the attainable adjustment of resistance, for thereby asmaller proportion of the total length of As the one convolution can beadded or cut oif by the same amount of circumferential movement of thefoot. Great speed and delicacy of adjustment is accordingly provided, inapparatus of extreme simplicity of construction, by the presentinvention inasmuch as the mere sliding of the shoe across the successivewindings gives a setting of the shoe on the turns of wire which isalmost correct so that but little movement around the winding isrequired to add or subtract the necessary amount of resistance to makethe adjustment perfect.

Although the preferred embodiment of the invention is herein illustratedas comprising a fixed coil and a movable brush, it is obvious that theprinciples could be applied as Well with a fixed brush and a movablecoil. Furthermore the invention is not limited to a coil arrangement,but its scope embraces any conductor having a series of adjacent linescontinuously connected and means whereby a second conductor may be movedrelative to the first from one line to another for large increase ordecrease of current path, and along any one line of the series forminute changes.

I claim as my invention:

1. A rheostat comprising a continuous resistance element, arranged insuccessive connected lines, combined with a brush element adapted toengage the resistance element palpably between any pair of adjacentlines thereof; one of said elements being mounted fixedly and the otherof them being mounted movably with respect to the fixed element andbeing manually movable in its said mounting so that, by its movementalone, the location of engagement of brushwith resistance is adjustableboth across and along said lines; the said engagement being such thatwhen the location of contact is adjusted along the lines the saidengagement may cause the contact to continue between the brush and theparticular pair of said lines which are at the moment engaged by thebrush.

2. A rheostat comprising a resistance coil, a brush; a support for thebrush; and axial mounting means for the support wherein the support ismovable longitudinally and rotatably, and whereby the brush is movablein three dimensions of space to various parts of the surface of thecoil; said brush and resistance material having surfaces which areconvex to each other making tangential contact in each of saiddirections.

3. A vernier rheostat having a helical resistance coil, a longitudinallymovable and rotary shaft arranged concentrically thereto, and a yieldingcontact carried by the shaft and movable thereby transversely andconcentrically with respect to the convolutions of the helical coil forthe coarse and fine regulation of the current, respectively.

4. A vernier rheostat having an insulating spool, a helical resistancecoil thereon, a longitudinally movable and rotary shaft passing throughthe center of the spool, a knob on the shaft, and a yielding contactcarried by the shaft and removable there by transversely andconcentrically with respect to the convolutions of the helical coil forthe coarse and fine regulation of the current, respectively.

Signed at Boston, Massachusetts, this second day of March, 1922.

JOSEPH A. ROSTRON.

Certificate of Correction.

Patent No. 1,620,573. Granted March 8 1927, to JOSEPH A. ROSTRON.

It is hereby certified that error appears in the printed specificationof the abovenumbered patent requiring correction as follows: Page 3,line 71, claim &, for the Word removable read movable; and that the saidLetters Patentshould be read with this correction therein that the samemay conform to the record of the case in the Patent Office.

Signed and sealed this 19th day of April, A. D. 1927.

[SEAL] M. J. MOORE,

Acting Commissioner of Patents.

Certificate of Correction.

Patent No. 1,620,573. Granted March 8, 1927, to JOSEPH A. ROSTRON.

It is here-by certified that error appears in the printed specificationof the abovenumbered patent requiring correction as follows: Page 3,line 71, claim 4, for the Word removable read movable; and that the saidLetters Patent should be read with this correction therein that the samemay conform to the record of the ease in the Patent Office.

Signed and sealed this 19th day of April, A. D. 1927.

[SEAL] M. J. MOORE,

Acting Cowvmz'ssioner of Patents.

